For the Los Angeles soirée, the actor, 57, dressed in a dark suit, white shirt and multicolored tie, while his girlfriend of four years, 49, stood out in a red halter style dress.
The pair held hands and even had a sweet moment on the carpet where they locked eyes while grinning ear to ear. Grant, an artist herself, mentioned the event via an Instagram post.
"So thrilled to be @moca last night to welcome and celebrate the new director Johanna Burton, the first female director of the museum," she captioned a photo from inside the celebration. "Together with recently appointed chief curator Clara Kim this promises a fresh direction in MOCA's support of artists through exhibitions, programming and publications."
"The artists Pipilotti Rist and Chance the Rapper reminded us about being together bravely humming and listening to our inner guidance," she added. "So grateful to be part of this community."
As OK! previously reported, the private pair — who met in 2011 while collaborating on Reeves' book Ode to Happiness – is rumored to be engaged, but they have yet to comment on the speculation.
"Keanu popped the question after they returned home from Europe, where he was filming back-to-back movies, and she was there the whole time to support him," an insider spilled two months ago. "That’s when he realized he can’t live without her."
"Alexandra is a huge light in his life," gushed another source. "Everyone can see how she fills him with joy."
It's unclear if the two have picked a date, but according to the buzz, the nuptials will be laid-back and intimate with just "a small group of family and friends" scoring invites.
"Of course, they’re writing their own vows," added the insider. "And no doubt it will get very emotional."